There is no way to directly control the RAM divider on K8 processors. If it is a little low you can try raising the 200MHz system clock a little bit to bring it in line.
Older processors used a FSB/RAM divider, the K8 family uses a Processor Freq/RAM Divider that is set for each cpu multiplier. If your processor freq and multiplier are falling to where the RAM is not running quite full speed, the only option is to increase the CPU speed by bringing the system clock (the 200MHz one) up a bit (like 2-6MHz). Don't overdo it, move it up slowly, and you may have to drop your HT multiplier from 5 to 4, HT on these chips did not like going much (at all, really) over 1000MHz.